Abstract: An important physiological function of mammary epithelial cells is to synthesize and secrete major nutrients of milk. As one important part of innate immunity, the role of mammary epitheliai cells played in prevention and therapy of mastitis received a wide publicity. Immunologic active material was researched by primary mammary epitheliai cell cultures and cell line, and the results showed that mammary epithelial cells can secrete a large number of immune-regulating factors when pathogens invade the mammary gland, such as chemokine，pro-inflammatory cytokine and host defense peptide. These immune active ingredients play an important role in mastitis occurrence and its development.

Key words: mammary epithelial cell; mastitis; immune-regulating factors